The present invention relates to a method and apparatus for determining fertility status of a female. More specifically, the invention relates to a method and apparatus for predicting ovulation and thereby determining the fertile phase from the non-fertile phase in the reproductive cycle of a female mammal, and preferably a female human.
The fertile phase in a mammal can be defined as the period during which sperm present in the uterus may encounter and fertilize an egg. Generally, in female humans, the average reproductive cycle is 28 days, of which a released egg survives only about 12 to 24 hours. However, the uterus is capable of storing sperm for a period of up to four days. Thus, the fertile phase can commence up to four days prior to ovulation and last for up to one day after ovulation. But, the time period following ovulation, when an egg is released, is relatively narrow.
Many prior art devices have been proposed to determine when ovulation has occurred. However, by merely determining when ovulation has occurred, these prior art devices and methods only determine a fraction of the fertile phase in a female human. Clearly, an advantage can be obtained by predicting ovulation at least four days in advance, which will encompass the entire fertile phase of a woman. In this way, pregnancy can be planned.
Several methods for determining ovulation have been proposed in the past. In female humans, the maturation of ovarian follicles which will eventually release a fertile egg are effected by the action of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) secreted by the anterior lobe of the pituitary. The ovulatory phase of the menstrual cycle is preceded by a significant rise in serum total estrogens 24 to 48 hours prior to ovulation, which prepare the uterus for possible implantation. The rise in estrogens is followed by a rapid rise in serum luteinizing hormone (LH) reaching a peak 12 to 24 hours prior to ovulation. Many other physiological conditions also change around the time of ovulation. For instance, basal body temperature (BBT) reaches a nadir followed by a sharp rise around the time of ovulation. Cervical mucus undergoes viscosity changes stimulated by rising estrogen which can help direct sperm towards the egg.
Several fertility detectors have been developed which measure these various hormones or their indirect physiological effects. The BBT method, referred to above, generally requires female humans to take their vaginal temperature and chart the value every morning before rising. Besides the considerable diligence involved, the method is generally only accurate within one to two days of ovulation, and gives no prior notice. Cervical mucus measurements have been regarded as somewhat more helpful. Women can examine their cervical mucus for a thinning of the mucus just before ovulation, which allows it to be drawn intact between the fingers and is referred to as the spinbarkeit reaction. Another method involves examining the cervical mucus under a microscope and looking for a xe2x80x9cferningxe2x80x9d reaction indicative of imminent ovulation. A further method measures vaginal mucus conductivity using impedance probes which allows a somewhat more quantitative estimation of the mucus changes as disclosed in U.S. Pat. No. 4,770,186. U.S. Pat. No. 5,209,238 to Sundhar discloses an ovulation monitor which determines the presence of a viable egg by sensing the mucous density, basil body temperature, and pH level and LH level of secretion in the vagina.
However, these prior art methods suffer from the disadvantage that they determine ovulation, but do not provide a means for predicting ovulation, thereby missing a large portion of the fertile phase. Also, cervical mucus examination suffers from subjective errors as well as being arduous and again gives little to no prior notice of ovulation.
U.S. Pat. No. 5,685,319 to Marett discloses that a significant pH nadir in female eccrine sweat was found to occur approximately five to six days prior to ovulation. In this way, tracking the pH of eccrine sweat could assist in predicting ovulation, and thereby determining the fertility status of a female human. Furthermore, an advantage of tracking pH is that it is inherently buffered in that the hydrogen ions H+ can react with the hydroxide ion (OH) to form water. In addition, even though there is no satisfactory mechanism to explain skin acidity, previous studies have found that eccrine sweat of women is also generally buffered by either the lactic acid/lactate system, free amino acid secretion or CO2 bicarbonate. The benefit of having the pH buffered is that changes in the quantity of eccrine sweat, such as through evaporation or increased physical activity, will not greatly affect the pH, thereby avoiding spurious readings.
Several researchers have also investigated changes of other ions in eccrine sweat. For instance, Lieberman and Taylor looked at chloride (Clxe2x88x92), sodium (Na+) and potassium (K+) in the eccrine sweat of female humans (Lieberman et al. JAMA Feb. 21, 1996, Vol. 195, No. 8, pages 117-123 and Taylor et al., Journal of Investigative Dermatology, Vol. 53, No. 3, pages 234-237, 1969). However, neither Lieberman nor Taylor investigated changes in the concentrations of these ions prior to ovulation and for the purpose of predicting ovulation.
One disadvantage of much of the prior art has been that it fails to predict ovulation at least three to six days in advance. Because of this, the prior art methods and devices fail to determine the entire fertile phase of a female.
Furthermore, other than for measuring pH, the prior art has failed to consider what other characteristics of eccrine sweat of female humans can be used to predict ovulation. The prior art has failed to provide a reliable and consistent method and device to obtain measurements of the characteristics of eccrine sweat, such as changes in the concentrations of ions, other than pH. In addition, the prior art has failed to provide a method and device which can measure changes in concentrations of ions in eccrine sweat which are not naturally buffered, as is pH, and which may therefore vary due to other factors, such as eccrine sweat volume due to increased physical activity, ambient temperature or evaporation.
Accordingly, there is a need in the art for a method and device to reliably and economically predict ovulation three to six days in advance in order to determine a larger portion of the fertile phase of a female mammal, and preferably a female human. There is also a need for a method and device to predict ovulation which is easy to use, reliable and inexpensive.
Accordingly, it is an object of this invention to at least partially overcome some of the disadvantages of the prior art. Also, it is an object of this invention to provide an improved method and device to assist in predicting ovulation in female mammals, and preferably female humans, about one to six days in advance, which is reliable and can be economically implemented.
Accordingly, in one of its aspects, this invention resides in a device for determining a fertile phase of a female human comprising: (a) a sensor for sensing concentrations of at least two ions in the eccrine sweat of the female and generating output signals indicative of concentrations of the at least two ions in the eccrine sweat; (b) a processor for controlling the sensor to sense the concentrations of at least two ions in the eccrine sweat substantially simultaneously and at least on a daily basis; and wherein the processor monitors the output signals from the sensor to identify a distinct change in the concentration of one of the at least two ions following an inversion which indicates the female human is in the fertile phase.
In a further aspect, the present invention resides in a device for determining the fertility status of a female mammal comprising: (a) a sensing means for sensing at least one ion selected from the group consisting of potassium (K+), ammonium (NH4+), calcium (Ca2+), chloride (Clxe2x88x92), nitrate (NO3) and sodium (Na+), in the eccrine sweat of the female mammal and generating output signals indicative of the concentration of ions in the eccrine sweat; (b) processor means for controlling the sensing means to sense the at least one ion in the eccrine sweat at least on a daily basis; and wherein the processor means monitors the output signals stored in the storage means to identify a distinct change in a concentration of one of the ions following an inversion which indicates the female mammal is in the fertile phase.
One advantage of the present invention is that changes in concentrations of several different types of ions in eccrine sweat can be sensed and analyzed to predict ovulation in female mammals. These ions include sodium (Na+), potassium (K+), ammonium (NH4+), calcium (Ca2+) and nitrate (NO3xe2x88x92). In this way, different types of sensors can be selected to sense the corresponding ions, such as sodium (Na+), chloride (Clxe2x88x92), ammonium (NH4+), potassium (K+), calcium (Ca2+) and nitrate (NO3xe2x88x92). In addition, sensors to sense the conductivity of eccrine sweat, thereby indirectly measuring the total concentration of all of the ions, can be used. This permits a selection to be made as to which sensor is most reliable for a particular situation.
For instance, in colder climates where the user may excrete less eccrine sweat, a different type of ion, and a different type of sensor, could be used than in warmer climates where more eccrine sweat is excreted. Likewise, in veterinarian use, different sensors to sense different ions could be used depending on the particular situation and mammal whose fertility status is being sensed. Furthermore, this permits the sensor to be selected based on features other than reliability, such as cost and availability.
A further advantage of the present invention is that it provides for measurement of changes in concentrations of more than one ion in eccrine sweat. In this way, the changes in concentration of two or more ions can be monitored to provide confirmatory readings in order to more accurately predict ovulation and avoid false readings due to non-hormonal effects such as eccrine sweat volume, diet and stress.
A further advantage of measuring changes in concentration of more than one ion in eccrine sweat is that ratiometric measurements can be obtained. For example, it has been discovered that sodium (Na+) and chloride (Clxe2x88x92) ions in eccrine sweat are the dominant ions and can be used to reference the rate of sweating. By using sodium (Na+) or chloride (Clxe2x88x92) as a reference ion, the concentration changes in other ions in relation to sodium (Na+) and chloride (Clxe2x88x92) can be assessed. The ratio of chloride (Clxe2x88x92) to sodium (Na+) is particularly constant, which is expected because chloride (Clxe2x88x92) is the main counter ion for sodium (Na+). While the concentrations of chloride (Clxe2x88x92) and sodium (Na+) ions can each be measured individually to predict ovulation, these ions can also be used in order to account for changes in concentrations of the other ions, such as potassium (K+), ammonium (NH4+), calcium (Ca2+) and nitrate (NO3xe2x88x92), due to changes in the quantity of eccrine sweat, such as through evaporation, increased ambient temperature, increased physical activity or ion accumulation on the skin over time. This is the case because while sodium (Na+) and chloride (Clxe2x88x92) surge prior to ovulation, they do not surge as much as other ions, such as nitrate (NO3xe2x88x92), calcium (Ca2+) and ammonium (NH4+). Accordingly, by performing a ratiometric measurement between one of the ions, such as potassium (K+), ammonium (NH4+), calcium (Ca2+) or nitrate (NO3xe2x88x92), with respect to either sodium (Na+) and/or chloride (Clxe2x88x92), a more consistent measurement of the ions can be obtained, and changes in concentration due to changes in eccrine sweat volume and ion accumulation on the skin over the day can be accounted for to some extent. In this way, a more accurate measurement can be made.
A still further advantage of the present invention is that some of the ions have been found to have counteracting effects. For instance, the concentration of calcium (Ca2+) has been found to change in the opposite direction during the time period of interest preceding ovulation. In this way, performing a ratiometric measurement of calcium (Ca2+) with respect to another ion, such as ammonium (NH4+), can improve prediction because a more pronounced effect will be monitored.
In order to further improve the prediction, three ions may be measured, such as ammonium (NH4+), calcium (Ca2+) and either sodium (Na+) or chloride (Clxe2x88x92). Measurements can then be made with respect to ammonium (NH4+) and sodium (Na+), as well as sodium (Na+) and calcium (Ca2+), to account for changes in concentrations of all of the ions due to accumulation on the skin or changes in eccrine sweat volume due to temperature and/or physical activity. These two ratiometric measurements can then be compared to obtain a ratiometric measurement of ammonium (NH4+) with respect to calcium (Ca2+), but with some of the changes due to other effects accounted for because the concentrations of ammonium (NH4+) and calcium (Ca2+) were initially measured with respect to sodium (Na+).
A further advantage of the present invention relates to one embodiment where the method is implemented by means of a device that is in contact with the skin for extended periods of time, such as 12 hours on a daily basis. This facilitates taking several readings over the course of a day so that a better statistical analysis can be performed. Furthermore, by taking several readings over the course of a day, spurious readings can be identified and eliminated. Furthermore, the device can, in a preferred embodiment, sense when it is not on the skin so that a reading will not be taken at this time. This obviously decreases the number of incorrect readings, while at the same time, not adversely affecting the overall daily reading, because a large number of other readings will likely be obtained during the course of the day and can be used to obtain a reliable average. In other words, by taking a large number of readings, such as 10 to 48, over a period of time, such as 24 hours, and statistically examining these readings, changes in eccrine sweat not related to menstrual hormones can be largely removed.
A still further advantage of the present invention is that readings from previous reproductive cycles can be stored for the same female. These stored readings can be used to better predict ovulation by ignoring readings taken during the early part of the reproductive cycle. For instance, if it is known from previous reproductive cycles that a particular female human never ovulates within four days of menstruation starting, the readings at the beginning of the reproductive cycle, following menstruation will be given less weight in predicting ovulation in the future. In a preferred embodiment, the duration of the reproductive cycle is determined and then, for female humans, ovulation is estimated to occur at some time in the last 19 days of the reproductive cycle. This coincides with the Luteal period which is generally 14 days from ovulation to menstruation for humans. Accordingly, the portion of the reproductive cycle prior to 19 days from the estimated start of menstruation is given less weight or disregarded for the purposes of determining the fertile phase of the female.
Further aspects of the invention will become apparent upon reading the following detailed description and drawings which illustrate the invention and the preferred embodiments of the invention.